EP3177379B1 - Column and process for the thermal treatment of a fluid, having a return line - Google Patents

Description

The present invention relates to a column for the thermal treatment of a fluid. The column has a cylindrical, vertically oriented column body which forms a column cavity, and a mass transfer tray arranged in the column cavity, which forms a collecting surface. The column is in particular a separation column. Furthermore, the invention relates to a thermal separation process between at least one gas rising in a column and at least one liquid descending in the column.

In separation columns, gaseous (ascending) and liquid (descending) streams are often passed in countercurrent, with at least one of the streams containing in particular a (meth) acrylic monomer. As a result of existing between the streams imbalances takes place a heat and mass transfer, which ultimately causes the desired separation in the separation column (or separation). In this document, such separation processes should be referred to as thermal separation processes.

Examples of and thus element of the term "thermal separation process" used in this document are the fractionating condensation (cf., for example, US Pat DE 19924532 A1 . DE 10243625 A1 and WO 2008/090190 A1 and the rectification (in both, ascending vapor phase is conducted in countercurrent to descending liquid phase, the separation effect being due to the vapor composition being different in equilibrium from the liquid composition), the absorption (at least one ascending gas is countercurrently fed to at least one descending liquid the separation effect is due to the different solubility of the gas constituents in the liquid) and the desorption (the reversal process for absorption; the gas dissolved in the liquid phase is separated by partial pressure reduction; the partial pressure reduction of the liquid phase solutes at least partially by passing a carrier gas through the liquid phase is passed, this thermal separation process is also referred to as stripping; alternatively or additionally (at the same time as a combination), the partial pressure reduction can be effected by lowering the working pressure).

For example, the separation of (meth) acrylic acid or (meth) acrolein from the product gas mixture of the catalytic gas phase oxidation can be carried out so that the (meth) acrylic acid or the (meth) acrolein by absorption into a solvent (eg water or an organic solvent ) or by fractional condensation of the product gas mixture first grundabgetrennt and that thereby resulting absorbate or condensate is subsequently further separated to obtain more or less pure (meth) acrylic acid or (meth) acrolein (cf., for example DE-10332758 A1 . DE 10243625 A1 . WO 2008/090190 A1 . DE 10336386 A1 . DE 19924532 A1 . DE 19924533 A1 . DE 102010001228 A1 . WO 2004/035514 A1 . EP 1125912 A2 . EP 982289 A2 . EP 982287 A1 and DE 10218419 A1 ).

The notation (meth) acrylic monomers in this document is abbreviated to "acrylic monomers and / or methacrylic monomers".

The term acrylic monomers is used in this document to shorten "acrolein, acrylic acid and / or esters of acrylic acid".

The term methacrylic monomers is used in this document to shorten "methacrolein, methacrylic acid and / or esters of methacrylic acid".

Specifically, the (meth) acrylic monomers contemplated herein are the following (meth) acrylic esters: hydroxyethylacrylate, hydroxyethylmethacrylate, hydroxypropylacrylate, hydroxypropylmethacrylate, glycidylacrylate, glycidylmethacrylate, methylacrylate, methylmethacrylate, n-butylacrylate, isobutylacrylate, isobutylmethacrylate, n-butylmethacrylate, tert-butyl acrylate, tert-butyl methacrylate, ethyl acrylate, ethyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, N, N-dimethylaminoethyl acrylate and N, N-dimethylaminoethyl methacrylate.

(Meth) acrylic monomers are important starting compounds for the preparation of polymers, e.g. be used as adhesives or as water super absorbent materials in hygiene articles use.

On a large scale, (meth) acrolein and (meth) acrylic acid are predominantly produced by catalytic gas phase oxidation of suitable C ₃ - / C ₄ precursor compounds (or precursor compounds thereof). In the case of acrolein and acrylic acid, propene and propane are preferably used as such precursor compounds. In the case of methacrylic acid and methacrolein, iso-butene and iso-butane are the preferred precursor compounds.

In addition to propene, propane, isobutene and isobutane, suitable starting materials are other compounds containing 3 or 4 carbon atoms, for example isobutanol, n-propanol or precursor compounds thereof, for example the methyl ether of isobutanol. Acrylic acid can also be obtained by gas-phase catalytic oxidation of Acrolein be produced. Methacrylic acid can also be produced by gas-phase catalytic oxidation of methacrolein.

In the context of such production processes, product gas mixtures are normally obtained, from which the (meth) acrylic acid or the (meth) acrolein must be separated off.

Esters of (meth) acrylic acid are e.g. by direct reaction of (meth) acrylic acid and / or (meth) acrolein with the corresponding alcohols. However, in this case as well, first product mixtures are obtained from which the (meth) acrylic acid esters have to be separated off.

The separation columns in which these separation processes are carried out contain separating internals. These pursue in the thermal separation process the purpose of increasing the surface area for the separation in the separation column causing heat and mass transfer ("the exchange surface").

As such internals come e.g. Packings, packing and / or trays, which are also referred to as mass transfer trays, into consideration. Often, the separation columns used are those which contain at least one sequence of mass transfer trays, at least as part of the separating internals.

Mass transfer trays pursue the purpose of providing areas in the separation column in the form of liquid layers which form on them, with substantially closed liquid phases. The surface of the rising in the liquid layer and thereby distributing in the liquid phase vapor or gas flow is then the relevant exchange surface.

A succession of mass transfer trays is understood to mean a succession (one after the other) of at least two superimposed in the separation column, generally identically constructed (i.e., identical), mass transfer trays. In terms of application technology, the clear distance between two mass transfer trays directly following one another in such a series (series) of mass transfer trays is made uniform (i.e., the mass transfer trays are arranged equidistantly in the separating column).

The simplest embodiment of a mass transfer tray is the so-called Regensiebboden. This is a plate or plate segments joined together to form a plate for the ascending gas or vapor phase (the Terms "gaseous" and "vaporous" are used synonymously in this document) distributed over the plate and substantially planar passage openings, eg round holes and / or slots, has (cf., eg DE 10230219 A1 . EP 1279429 A1 . US-A 3988213 and EP 1029573 A1 ). Exceeding openings (eg at least one downcomer (at least one drain segment)) do not have rain screen bottoms. As a result of this absence of downcomers, both the gas ascending in the separation column (the vapor rising in the separation column) and the liquid descending in the separation column must move oppositely in the temporal change through the (same) passage openings (through the open cross sections of the passage points) , One also speaks of the "dual-flow" of rising gas and descending liquid through the passage openings, which is why in the literature for such mass transfer trays often the term "dual-flow trays" is used.

The cross section of the passages of a dual-flow tray is adapted in a conventional manner its load. If it is too small, the ascending gas flows through the passage openings at such a high speed that the liquid descending in the separation column is entrained substantially without separation effect. If the cross section of the passages is too large, ascending gas and descending liquid move past one another substantially without replacement, and the mass transfer tray runs the risk of running dry.

That is, the separating effective working area of a Regensiebbodens (dual-flow floor) has two limits. A minimum limit speed of the rising gas must be given so that a certain liquid layer is held on the Regensiebboden to allow a segregation work of Regensiebbodens. The upper limit of the velocity of the rising gas is determined by the flood point, when the gas velocity leads to congestion of the liquid on the Regensiebboden and their rain is prevented.

The longest extent of the passage openings of a technical dual-flow tray (= longest direct connecting line of two points lying on the outline of the cross section of the passage opening) is typically 10 to 80 mm (cf., for example DE 10156988 A1 ). Normally, the passages within a rain screen are identical (ie, they all have the same geometric shape and cross section (cross sectional area)). In terms of application, its cross-sectional areas are circles. That is, preferred passages of Regensiebböden are circular holes. The relative arrangement of the passage openings of a Regensiebbodens advantageously follows a strict triangular division (cf., eg DE 10230219 A1 ). Of course, the passage openings within one and the same Regensiebbodens can also be designed differently (vary over the Regensiebboden).

In terms of application technology, a sequence of rain sieve bottoms in a separation column comprises identical (identical) rain sieve trays, which are preferably arranged equidistantly one above the other.

According to the DE 10156988 A1 but can also sequences of Regensiebböden be used in separation columns, the cross-section (preferably circular) within a dual-flow tray Although designed uniform, but within the sequence varies (eg decreases from bottom to top).

In general, each dual-flow bottom of a corresponding bottom sequence concludes flush with the wall of the separation column. But there are also variants in which there is a gap between column wall and floor, which is only partially interrupted by bridges. In addition to the actual passage openings, a Regensiebboden usually has at most still openings, which serve the attachment of the soil Auflageringen or the like (see, eg DE 10159823 A1 ).

In the normal operating range of a series of rain screen bottoms, the liquid descending in the separation column drops into drops from dual flow soil to dual flow soil, i.e., the gas phase rising between the dual flow trays is traversed by a split liquid phase. The falling on the respective bottom Regensiebboden drops are partially sprayed on impact. The gas stream flowing through the passage openings bubbles through the liquid layer formed on the surface of the floor, whereby an intensive mass and heat exchange takes place between the liquid and the gas.

Depending on the liquid and gas load, rain sieve trays with a column diameter of> 2 m tend to cause small uneven distributions of liquids to swell and thus liquid uptake of a soil can fluctuate over a large area or a rotating wave can form, resulting in a negative mechanical stability of the column body on the other hand, the separation effect is reduced, since the liquid distribution under these conditions is then greatly different in time and place. To avoid such instationarities, it has therefore proved to be advantageous to distribute flow breakers in the form of vertical plates on the bottom cross-section, which prevent or at least greatly reduce the swirling of the liquid within the column body. The height of the sheets should correspond approximately to the height of the forming liquid bubbling layer. This is about 20 cm under normal loads.

The cross section of a separation column is usually circular. This applies in a corresponding manner to the associated mass transfer trays.

For the purposes of this document usable dual-flow trays are eg in Technical Progress Reports, Vol. 61, Fundamentals of the Dimensioning of Column Trays, pages 198 to 211, Verlag Theodor Steinkopf, Dresden (1967 ) and in the DE 10230219 A1 described.

From the above-described sequence of rain screen bottoms comprising mass transfer trays without restraint of the bottom descending liquid on the bottom, sequences of mass transfer trays are distinguished with such liquid forced feed.

These mass transfer trays are characterized in that they additionally have at least one downcomer in addition to the passage openings already described. This is at least one drainage opening located in the mass transfer tray, which retains the liquid (eg, a drain weir (this may in the simplest embodiment extend the drain opening with a throat (a chimney, in the case of a circular drain opening of a tube) above)), and which drains into a passage tapering to the mass transfer tray below, which is generally center-symmetrical to an axis pointing in the column longitudinal direction. The cross-section of the well may vary along this axis (e.g., taper) or be constant.

Through the at least one downcomer of the mass transfer tray, the liquid descending from a higher mass transfer tray can, within a sequence of such mass transfer trays, continue as an at least one feed of liquid to the next lower mass transfer tray of the sequence, regardless of the gas or vapor still rising through the passages of that mass transfer tray dismount.

The essential basis for this separation of the flow paths of descending liquid and rising gas is the hydraulic closure (the liquid closure or shaft closure) of the respective downcomer for the rising gas (a downcomer must not bypass the rising gas Make passageways past; the gas flow (the steam flow) must not rise through a drainage shaft past the passage openings).

Such a hydraulic lock can e.g. can be achieved by pulling the downcomer downwards (so far downwards) that it dives deep enough into the liquid layer located on the next lower mass transfer tray of the sequence (such a closure is also referred to in this document as " static closure "). The liquid level required for this purpose can be determined on the lower mass transfer tray, e.g. be ensured by the height of appropriate drainage weirs.

However, such an embodiment has the disadvantage that the region of the lower mass transfer tray, which is located directly below the outlet cross section of a downcomer of the overlying mass transfer tray (the so-called inflow surface), can not have any passage openings for the rising gas and so not for the substance and heat exchange is provided between the liquid layer formed on the lower mass transfer tray and the rising gas.

In an alternative embodiment, the lower outlet end of the downcomer is raised so far that it no longer dips into the liquid layer located on the underlying mass transfer tray. In this case, between the lower end of the at least one downcomer and the mass transfer tray, to which the downcomer tapers, a sufficiently large gap, in which form a bubble layer and a mass and heat exchange between a (on the lower mass transfer tray) accumulating liquid layer and a gas (rising through this floor) can take place. That is, in this case, the "inflow area" of the at least one downcomer on the mass transfer tray below may also have through openings, thus increasing the available exchange area of the mass transfer tray, and thus its separating effect.

A static fluid closure of the downcomer can be effected in this case, for example, by means of a mounted below the outlet end of the downcomer collecting cup. In terms of application technology, in this case, the jacket wall of the collecting cup is pulled up so far that the outlet end of the downcomer dips into the collecting cup (it is also possible to allow the bottom edge of the downcomer to end at the upper edge of the collecting cup). When operating the column collects in the collecting cup which flows down through the downcomer Liquid until it flows over the upper edge of the shell wall of the collecting cup. The lower edge of the downcomer dives into the liquid contained in the collecting cup and the collecting cup forms a siphon-like liquid closure of the downcomer.

Alternatively, a raised drainage shaft can also be closed dynamically. For this purpose, the downcomer can be closed, for example at its lower end with a bottom which is provided with outlet openings which are dimensioned so that the liquid dammed in the downcomer and the penetration of gas is prevented (see, eg EP 0882481 A1 and DE 10257915 A1 ). In this case, the shaft closure is produced dynamically by the pressure loss that arises at the outlet openings. That is, in the static seal, the closure of the drainage shaft is characterized in that its outlet end immersed in jammed liquid, and dynamic closure effect constructive features at the outlet end of the downcomer that the exiting (leaking) liquid suffers a pressure loss in the downcomer backlog in selbigem descending liquid causes, which causes the closure. In the simplest case, such a pressure loss can be caused by the fact that one selects the cross section of the outlet opening of the downcomer small compared to the average cross section of the shaft.

For a separation-effective operation of a sequence of such mass transfer trays, the execution of the at least one downcomer is relevant. On the one hand, the cross-section of the at least one downcomer must be sufficiently large (usually the corresponding cross-sectional area is greater than the cross-sectional area of a passage opening), so that the liquid can safely descend through the at least one downcomer even at the maximum load of the separation column does not back up to the overlying ground. On the other hand, it must be ensured that the hydraulic closure of the at least one downcomer still exists even with minimal liquid load.

At low gas load there is also the risk of raining through of the liquid through the openings. In addition, the liquid in a downcomer must be able to accumulate until the weight of the dammed liquid column is sufficient to carry the liquid into the headspace below the mass transfer tray associated with the downcomer. This backwater height determines the minimum required length of the downcomer and thus determines the ground clearance required in a sequence of corresponding mass transfer trays. Significant contribution factor for the projected backwater level (backwater length) the pressure drop Δ P of a mass transfer tray. This pressure loss is suffered by the rising gas as it flows through the passages and the "hydrostatic" height of the bubble layer on the mass transfer tray. He is responsible for increasing the pressure in the gas phase of a sequence of such mass transfer trays from top to bottom. For the "hydrostatic" pressure h _p of the liquid accumulated in the downcomer of a mass transfer tray, therefore, at least the condition h _p > Δ P of the mass transfer tray must be met. These relationships are the expert from the example EP 1704906 A1 also known as the ability to ensure with a Zulwehrwehr on the deeper mass transfer soil that with static closure of the downcomer of the upstream mass transfer tray in the liquid layer on the deeper mass transfer tray, the shaft closure even under low load with descending liquid still exists. However, the use of a Zulaufwehrs increases the backwater level, which is required in the downcomer to push the jammed in the same liquid on the lower mass transfer soil. Overall, the element of the downcomer allows a widening of the separating working area compared to Regensiebboden. A favorable flow rate of the liquid accumulated in the downcomer out of the downcomer in the process according to the invention is, for example, 1.2 m / s.

In addition, it allows positive guidance of the descending on a mass transfer soil liquid on this floor.

For example, B. only one half of a (preferably circular) mass transfer tray at least one downcomer (ie, all drain holes are located with their full extent within the corresponding circle segment) and are arranged in a sequence of at least two identical such mass transfer trays the mass transfer trays in a separation column one above the other in that two top-to-bottom successive mass transfer trays in the separating column are each rotated by 180 ° about the column longitudinal axis (rotated) so that their downcomers are on opposite sides (in opposite halves) of the separating column the liquid descending from an upper mass transfer tray through its at least one downcomer to the mass transfer tray below it, on said lower mass transfer tray, over the lower mass transfer tray viewed from the at least one inlet surface of at least one downcomer of the upper (of the above attached) mass transfer tray (from the at least one inlet through the at least one downcomer of the upper mass transfer tray) in a necessary manner (ie, forced) to the at least one downcomer this flow in the lower mass transfer tray. That is, the liquid descending from the upper floor to the lower floor is forcibly led across the floor from the at least one inlet to the at least one outlet.

Such a liquid guide on a mass transfer tray within a sequence of identical mass transfer trays shall be referred to herein as a cross flow, the sequence of such identical mass transfer trays as a succession of identical cross flow mass transfer trays and the single mass transfer tray within the sequence as cross flow mass transfer trays.

In the simplest case, the cross-flow mass transfer tray is a cross-flow sieve tray. Apart from the at least one downcomer, it has passage openings for the gas rising in a separating column, for the design of which basically all the embodiments mentioned in the rain screen floor come into consideration. Preferably, a cross-flow sieve bottom as through-openings also has circular bores which, in terms of application technology, advantageously also have a uniform radius. As already mentioned, the at least one downcomer makes it possible for the liquid descending in a separation column to pass through a succession of crossflow trays independently of the flow path of the successive rising vapor (through the passage openings) from a higher crossflow sieve tray to the next descend lower-lying cross-flow sieve tray can. On the lower floor, the liquid flows in cross-flow from the at least one inlet of the lower floor formed by the at least one outlet of the higher cross-sieve tray to the at least one downcomer (to the at least one drain) of the lower floor, e.g. the height of at least one drain weir, via which the liquid can flow to the at least one downcomer, ensures the desired liquid level on the lower cross-flow sieve bottom. In addition, the liquid is held by the back pressure of the rising in the separation column steam on the cross-flow sieve tray. However, if the vapor load of a cross-flow sieve tray drops below a minimum value, the liquid may rain through the passage openings, which reduces the separating effect of the cross-flow sieve tray and / or leads to dry running of the cross-flow sieve tray.

This danger of dry running can be counteracted by the fact that the drain opening of the at least one downcomer is drained and the respective passage opening is extended upwards by a neck (a chimney, in the case of a circular passage opening of a tube).

Above the neck end, steam diverter hoods (bells, upturned cups) are usually attached (in the simplest case these can be bolted to the neck (e.g., front and back) and are practically slipped over the neck) which dip into the liquid accumulated on the floor. The rising through the respective passage opening steam first flows through the neck into the associated hood, in which it is diverted to then, in contrast to the cross-flow sieve bottom, parallel to the bottom surface of the hood in the self-accumulated liquid to flow (such "Parallel outflow" in the process according to the invention is generally advantageous insofar as it can "blow off" polymer particles formed in an undesired manner and thereby cause a self-cleaning effect). The gas streams (vapor streams) emerging from neighboring hoods, which are preferably distributed equidistantly over the trays, swirl the liquid accumulated on the bottom and form a bubbling layer in the same, in which the material and heat exchange takes place. Such cross-flow mass transfer trays are also referred to as cross-flow bubble trays or cross-flow tray trays. Since they also contain liquid accumulated with low rising gas (vapor) and thus run the risk of running dry, they are also referred to as hydraulically sealed cross flow trays. In comparison to cross-flow sieve trays, they usually require higher investment costs and cause higher pressure losses of the gas rising through them. In contrast to the simple sieve passage opening of a sieve tray, the passage opening of these trays, which is designed as described, is also referred to as bell passage opening or hood passage opening.

The most important component of the cross-flow bubble tray is the bell (cf. DE 10243625 A1 and Chemie-Ing.-Techn. 45th anniversary 1973 / no. 9 + 10, pp. 617-620 ). Depending on the shape and arrangement of the bells (Dampfumlenkhauben, hoods) distinguishes cross flow bell bottoms z. B. in crossflow Rundblockenböden (the cross sections of the passage opening, chimney (neck) and bell (Dampfumlenkhaube) are round (eg the cylinder bell bottom or the flat bubble bottom), tunnel cross flow trays (the cross sections of the passage opening, chimney and bell (hood) are rectangular, the passage points with their bells are arranged inside adjacent rows one behind the other, with the longer rectangular edge aligned parallel to the cross-flow direction of the liquid) and cross-flow Thormann® floors (the cross-sections of the passage opening, chimney and bell (hood) are rectangular, the passage points with their bells are arranged one behind the other within rows arranged next to one another, the longer rectangular edge being oriented perpendicular to the transverse flow direction of the liquid.) are z. B. in the DE 19924532 A1 and in the DE 10243625 A1 and the prior art appreciated in these two documents.

The bell edge can have very different shapes in cross-flow bubble trays (see. DE 10243625 A1 and Chemie-Ing. Techn. 45th Jahrg. 1973 / Nr. 9 + 10, pp. 617-620 ). Figure 3 out Chemie-Ing. Techn. 45 years. 1973 / No. 9 + 10, p. 618 shows some examples of the serrated and slotted edge. The serrations and slots are usually shaped so that the steam entering the mass stored on the mass transfer tray out of the bell dissolves as easily as possible into a large number of bubbles or jets of steam. The aforementioned Figure 3 as well as different figures of the DE 10243625 A1 also show exemplary embodiments of bell rims having a sawtooth-like structure, the teeth of which are additionally provided with vanes (baffles) ("raised slots"). The guide vanes are to impose a tangential exit direction on the gas stream (vapor stream) emerging from the bent sawtooth-like slots (direct the gas exit into the liquid in an oblique direction), whereby the surrounding liquid receives a directed impulse of movement, which interacts with the arrangement of the bells (steam deflection hoods). can result in a directional liquid flow on the cross-flow bubble tray overlaying the cross-flow established across the mass transfer tray (often such upturned slots are also referred to as drive slots). For example, in a sequence of cross-flow Thormann floors, the liquid does not flow on a lower cross-flow Thormann bottom directly across the ground, but driven in a manner described above, meandering from the at least one inlet to the at least one drain. The space between two cross-flow directionally arranged hoods of a cross-flow Thormannbodens each forms a groove in which the liquid flows. The details of a cross-flow Thormannbodens also usually carried out so that the liquid flows in two in the cross-flow direction each successive grooves in countercurrent (see, eg. FIG. 3 the DE 10243625 A1 ). The resulting meandering of the cross-flow extends the flow path of the liquid from the at least one inlet to the at least one drain, which favors the separation effect of a cross-flow Thormannbodens.

As already stated, in a cross-flow bubble tray, the gas emerging from the bell, in contrast to the cross-flow sieve bottom, is introduced parallel to the bottom surface in the liquid accumulated on the crossflow bubble tray. Frictional and buoyant forces then ensure that with increasing distance of the leaked gas flow from the bell edge more and more partial flows of the same in one direction be deflected perpendicular to the crossflow bell bottom and finally escape from the liquid layer. As the gas loading of a bell increases, the velocity of the gas stream leaving it increases, which increases the distance from the edge of the bell ("the area of action of the bell") up to which deflection has been described above.

This dependence of the effective range of a rigid bell on the gas load can be counteracted by configuring (executing) the passage opening of a cross-flow mass transfer tray as a valve (as a valve passage opening). The resulting cross-flow mass transfer trays are referred to as cross-flow valve trays (cf., for example, US Pat. DD 279822 A1 . DD 216633 A1 and DE 102010001228 A1 ).

The term cross-flow valve floors subsumes in this document thus cross-flow mass transfer trays, the passage openings (bottom holes) with stroke-limited plate, ballast or lifting valves (floating flaps) that adjust the size of the steam passage opening of the respective column load.

In a simple embodiment, the passage openings of the bottom for the aforementioned purpose with upwardly movable lids or plates (discs) are covered. During the passage of the rising gas, the lids (plates, disks) are raised by the gas flow in an additionally via the respective passage opening mounted (which is usually firmly anchored to the ground) corresponding guide frame (guide cage) and finally reach a gas load corresponding lifting height (instead of Guide cage, the disc can also have anchored with the floor upwardly movable valve legs whose upward mobility is limited upwards). The ascending through the passage opening gas flow is deflected at the bottom of the raised lid (plate, disc) in a similar manner as in the bell (at a bell passage opening) and emerges from the under the raised plate (lid, disc) resulting emergence area and as in the Bubble tray parallel to the bottom into the liquid stored on it. The plate stroke thus controls the size of the gas outlet area and adapts itself to the column load until the upper end of the guide cage limits the maximum possible lifting height. The plates may have downwardly directed spacers, so that at low gas load, the valve closes only so far that created by the spacers space still allows intensive mixing of the horizontal gas outflow with the cross-flow liquid. Spacers also counteract adhesion of the valve disc on the ground. By suitable design of the valve elements of a cross-flow valve bottom, the Adjusted blowing direction of the valve element and thus the liquid forced operation on the cross-flow valve bottom are additionally influenced (see, for. DD 216 633 A1 ). The principle of cross-flow valve trays and usable for the purposes of the present document valve bottoms is found, for. In Technical Progress Reports, Volume 61, Fundamentals of Column Sizing, pages 96 to 138 executed. In addition to the above-described movable valves, the expert also knows fixed valves. These are usually disc-shaped, or trapezoidal, or rectangular units that are punched out of the bottom plate and connected to it via upstanding fixed legs.

Especially with larger diameters of a separation column is formed on cross-flow mass transfer trays from the at least one inlet starting to reach the drain weir of the at least one course in a natural way to be observed liquid gradient (the gradient of the damming height of the liquid feeds (conditionally) the cross flow). This has the consequence that in areas with a lower liquid level due to the resulting lower resistances of the rising vapor (the rising gas) can relatively easily pass through the liquid layer. This can eventually result in an uneven gas load of the cross-flow mass transfer tray (the areas with a lower liquid height (a lower flow resistance) are preferably flowed through), which affects the separation effect thereof. By the application of z. B. in their seat height adjustable bells (alternatively, the bell size can be changed) in cross-flow bubble trays or by using z. B. plates (lids) with different weight at cross-flow valve floors can be compensated in this regard, so that the mass transfer floor over its cross-section substantially uniform guest (where the liquid level is smaller on the cross-flow mass transfer tray, the seat height of the bell is appropriate in terms of application The seat height of the bell can also be set deeper, for example, by shortening the length of the corresponding chimney, at the end of which the bell may be screwed, in a targeted manner, or alternatively, by shortening the weight of the lifting plate (lifting lid) or additionally, for example, the prong / slot structure of the bellhousing may also be varied to provide the desired flow resistance compensation, ideally, adjustment via the crossflow mass transfer tray is such that, during operation of the separation column, each of those on a crossflow bell bottom n bell located causes the same flow resistance for the rising gas). Incidentally, the passages (the passages) a cross-flow mass transfer tray usually advantageous designed uniformly.

Through a cross-flow mass transfer tray through openings extending (from top to bottom), the cross-sectional area usually more than 200 times smaller than the total cross-sectional area of all other openings of the Querstromstoffaustauschbodens (not including the cross section of the at least one downcomer), do not form (effective) through-openings the rising through the cross-flow mass transfer tray gas and self selbigen therefore not be attributed. For example, such openings may be tiny idle bores through which hydraulically sealed crossflow trays may run empty when a separation column is switched off. Also, such openings can serve Verschraubungszwecken.

Sequences of at least one downcomer having mass transfer trays in which the at least one inlet and the at least one sequence z. B. in the same half of the (circular) mass transfer tray or in which there is at least one inlet in the middle of the floor and the at least one drain at the edge of the soil, do not form a sequence of cross-flow mass transfer soils in the registration (inventive) sense.

The efficiency of cross-flow mass transfer trays designed as described is usually below that of a theoretical tray (a theoretical plate separator). As the theoretical soil (or theoretical separation stage) is to be understood in this document quite generally that one unit of space used for a thermal separation process, separating internals containing separation column, which causes a material enrichment in accordance with the thermodynamic equilibrium. D. h., The concept of the theoretical soil is applicable to both separation columns with mass transfer trays, as well as on separation columns with packings and / or packing.

The prior art recommends the use of sequences of at least two structurally identical (identically designed) cross-flow mass transfer trays including separating columns containing separation internals which are used to carry out thermal separation processes between at least one gas stream rising in the separation column and at least one liquid stream descending in the separation column and at least one of the streams contains at least one (meth) acrylic monomer. For example, the writings recommend DE 19924532 A1 . DE 10243625 A1 and WO 2008/090190 A1 the concomitant use of a sequence identical in construction hydraulically sealed cross-flow mass transfer trays in a separation column for carrying out a process of fractional condensation of a product gas mixture containing acrylic acid of a heterogeneously catalyzed gas phase partial oxidation of C ₃ precursors of acrylic acid with molecular oxygen, from bottom to top initially dual-flow trays and subsequently it contains hydraulically sealed cross-flow mass transfer trays.

Characteristic of the sequences of the cross-flow mass transfer trays recommended in the prior art is that the lower of two consecutive crossflow mass transfer trays in the direction of the cross flow from its at least one inlet to its at least one downcomer only in the region between the at least one inlet and the at least one downcomer (the at least one drainage opening) has passage openings (cf., for example, FIGS Figures 3 and 4 the DE 10243625 A1 , the FIG. 1 the DD 279822 A1 , the FIG. 1 the DD 216633 A1 and the illustration 1 out Chemie-Ing.-Techn. Volume 45, 1973 / No. 9 + 10, pages 617 to 620 ).

In the EP 2460577 A1 is described an oil wash column. In this oil wash column, a collected liquid phase is withdrawn via a side draw and fed into a reservoir. From the reservoir the cooled via a heat exchanger pure liquid phase the gasoline section is given up as return. The return takes place on a valve bottom, which is arranged two floors above the lowermost valve bottom, in which the lateral trigger is arranged.

The CA 2017980 A1 describes a distillation reactor in which a catalyst is replaced by a fresh or regenerated catalyst. For this purpose, the liquid catalyst, which has collected on a collecting tray, removed via an outlet. The withdrawn catalyst is fed to a separator in which solid components of the catalyst are separated. The liquid catalyst is pumped back to the distillation reactor. For this purpose, a return opening is provided, which is arranged below the removal of the catalyst.

Furthermore, the describes DE 19924532 A1 a process of fractionally condensing an acrylic acid-containing product gas mixture of a heterogeneously catalyzed gas-phase partial oxidation of C3 precursors of acrylic acid with molecular oxygen. The separation column used has both dual-flow trays and hydraulically sealed crossflow trays as separation-effective internals.

Another column for separating dust is in the US 2,141,829 described.

Finally, that describes EP 00009545 a process for recovering acrylic acid from a gaseous reactor effluent containing acrylic acid, acrolein, water and impurities.

A problematic property of (meth) acrylic monomers is their tendency to undesired polymerization, which, especially in the liquid phase, can not be completely suppressed even by the addition of polymerization inhibitors.

A disadvantage of known separation columns is that, when the thermal separation process is carried out continuously over a longer period of operation, the mass transfer trays are comparatively frequently used to form unwanted polymer. This is particularly disadvantageous because the operator of the thermal separation process due to the unwanted Polymerisatbildung must interrupt the thermal separation process again and again to remove the polymer formed. The same can indeed partially or completely close the passages of the mass transfer tray. In addition, radical polymerization of (meth) acrylic monomers is usually highly exothermic, i. H. under strong heat. There is a risk that the polymerization proceeds so vigorously that the separation column containing the polymerization mixture explodes.

It is an object of the present invention to provide a column and a thermal separation process of the type mentioned above in which polymerization of the substance present in the separation column can be prevented or at least reduced.

According to the invention this object is achieved by a column having the features of claim 1 and a thermal separation method having the features of claim 13. Advantageous embodiments and further developments emerge from the dependent claims.

Accordingly, the invention relates to a column for the thermal treatment of a fluid having a cylindrical, vertically oriented column body, which forms a column cavity, and a mass transfer tray arranged in the column cavity, which forms a collecting surface. The column according to the invention further comprises a circulation device having at least one drain opening formed in the column body above the collection surface, a circulation line in fluid communication with the drain opening and at least one return port fluidly connected to the circulation line and formed in the column body above the collection surface.

The spatial terms "top", "bottom", "horizontal" and "vertical", unless explicitly stated otherwise, refer to the orientation of the column during operation.

It has been found that the undesired polymer is formed in particular in so-called dead zones of the mass transfer tray. In such dead zones, the residence time of the fluid in the mass transfer tray is particularly long. Such a long residence time favors the polymerization. By provided in the column of the invention circulation means, a liquid circulation can be generated on the collecting surface of the mass transfer tray, which avoids the formation of dead zones. The liquid stream takes with it any fluid residues. The residence time of liquid on the collecting surface of the mass transfer tray is thereby reduced. In particular, the residence time distribution becomes narrower, that is, there are fewer volumes of liquid remaining on the mass transfer tray for a longer time. Advantageously, this can prevent the polymer from partially or completely closing through openings in the mass transfer tray. In addition, the risk of explosion caused by the polymerization mixture is reduced.

According to one embodiment of the column according to the invention, the drain opening is arranged directly above the lowest area of the collecting surface of the mass transfer tray. In particular, the lower edge of the discharge opening may be arranged at the same height as the deepest region of the collecting surface, so that the liquid located on the collecting surface is substantially completely to the discharge opening can run without residues remaining on the collecting surface. Advantageously, this effectively prevents the formation of polymer when a fluid is treated in the column which tends to polymerize.

According to one embodiment of the column according to the invention a plurality of vertically spaced mass transfer trays are arranged in the column cavity and the discharge opening and the return opening are arranged vertically between two adjacent vertically spaced mass transfer trays. In this case, in particular, the ratio of the vertical distance of the deepest portion of the collecting surface of the mass transfer tray from the lower edge of the discharge port to the vertical distance of the deepest portion of the collecting surface of the mass transfer tray from the bottom of the overlying mass transfer tray is in a range of 0 to 0.3 , in particular in a range of 0 to 0.1.

The return opening can open in the column according to the invention either above the drain opening in the column cavity or the return opening opens at the same height as the drain opening in the column cavity. Advantageously, the arrangement of the return opening is selected relative to the drain opening so that on the collecting surface of the mass transfer tray, a liquid circulation is generated, which reaches all areas of the mass transfer tray, so that in particular form no dead zones.

According to one embodiment of the column according to the invention, the ratio of the vertical distance of the deepest portion of the mass transfer tray collecting surface from the upper edge of the return aperture to the vertical distance of the lowest portion of the mass transfer tray collecting surface from the bottom of the immediately above the mass transfer tray is in a range of 0 to 0.3, in particular in a range of 0 to 0.2. These geometric conditions advantageously ensure that the liquid is usually introduced below the liquid level on the collecting surface. The return opening is also arranged in particular directly above the lowest region of the collecting surface of the mass transfer tray. In this way, advantageously, a particularly good mixing of the liquid can be achieved on the collecting surface of the mass transfer tray.

According to a development of the column according to the invention, a nozzle for generating a liquid jet when the liquid enters the column cavity is arranged in the return opening. If several return openings are arranged in the column, in particular each of these return openings can have such a nozzle. By means of the nozzle or the nozzles can be prevented even more effectively that dead zones arise, in which polymer is formed in the treatment of a corresponding fluid.

The circulation line and the return opening or the return openings are in particular arranged so that the recirculated liquid enters radially into the column cavity. Advantageously, this more effectively prevents the formation of dead zones.

According to a development of the column according to the invention a plurality of spaced apart return openings are formed in the column body. These return openings are each in fluid communication with the circulation line. The liquid discharged via the drainage opening can in this way be recycled to the column cavity above the mass transfer tray at several points. Advantageously, this makes it even more effective that no dead zones form at the collecting tray.

In the column according to the invention, the mass transfer tray or at least one bottom of the column has passage openings for gas rising from below. In these passages, cylindrical bodies extend upwards. These cylindrical bodies are provided in particular at a certain distance with hoods, caps or roofs, so that gas can escape laterally from the cylindrical bodies, without the abraschende from the overlying mass transfer medium liquid can move in countercurrent to the gas. These bodies, also referred to as chimneys, which are perpendicular to the mass transfer tray, may in special cases have a square, rectangular, elliptical cross-sectional area in addition to a circular cross-section. The distance (A) of the hoods, caps or roofs to the cylindrical body with diameter (D) is usually A <2D. This type of floor is a chimney floor, which collects at least part of the fluid dissipating from the upper floor in the space between the chimneys, where it can be fed from there to a purposeful other use.

According to one embodiment of the column according to the invention, the upper edges of the cylindrical body form overflow edges. The ratio of the vertical distance of the lowest area of the collecting surface of the mass transfer tray from the lower edge of the discharge opening to the vertical distance of the lowest region of the collecting surface of the mass transfer tray from the height of the lowest overflow edge of the cylindrical body is z. B. in a range of 0 to 0.1, in particular in one Range from 0 to 0.05. In the column of the present invention, the ratio of the vertical distance of the deepest portion of the mass transfer tray collecting surface from the upper edge of the return port to the vertical distance of the deepest portion of the mass transfer tray collecting surface from the height of the lowermost overflow edge of the cylindrical bodies is in a range of 0 to 0 , 9, in particular in a range of 0 to 0.3. These geometric conditions advantageously ensure that the liquid is usually introduced below the liquid level on the collecting surface. In this way, advantageously, a particularly good mixing of the liquid in the areas between the cylindrical bodies can be achieved.

In an embodiment according to the invention of this bottom, the return openings are arranged relative to the cylindrical bodies so that a meandering liquid flow results on the collecting surface of the mass transfer tray. In this way, the liquid flow can in particular reach all areas of the collection surface on the mass transfer tray so that no dead zones form on the collecting surface despite the interruptions by the cylindrical bodies.

According to a development of the column according to the invention, the circulation line has a junction for supplying a further liquid. In particular, an inert liquid or a liquid with polymerization inhibitors is supplied via this junction.

In particular, a pump is arranged in the circulation line with which liquid accumulating on the collecting surface of the mass transfer tray can be pumped off and this can be fed back to the column cavity through the return opening. By means of the pump or an additional control valve, the liquid flow can be controlled or regulated on the mass transfer tray. The pump or control valve may be further coupled to a sensor which measures the level of liquid on the collecting surface of the mass transfer tray. Depending on this liquid level, the pump can then regulate the circulation and / or the liquid removal of the liquid.

The column according to the invention can be used in particular as a separation column. The separation column has a sequence of mass transfer trays. As mass transfer trays in particular the floors mentioned above are used, ie mass transfer trays without forced operation, such as rain screen floors and dual-flow trays, and mass transfer trays with a liquid forced operation, such. B. crossflow mass transfer trays, in particular cross-flow bell bottoms, cross-flow hood bottoms, cross-flow thormann bottoms and cross-flow valve bottoms.

The clear distance between two directly successive trays within the column according to the invention is in particular not more than 700 mm, preferably not more than 600 mm or not more than 500 mm. In terms of application, the clear distance within the floor sequence is 300 to 500 mm. As a rule, the ground clearance should not be less than 250 mm.

The height of the column body is, for example, greater than 5 m, in particular greater than 10 m. However, it is also possible that the height of the column body exceeds 30 m or 40 m.

Between the floors further separation-effective internals can be arranged. Due to the separating internals, the separation of substances in the separation column is improved. These further installations can be provided, for example, in the form of packages, in particular structured or ordered packages, and / or fillings. Among the beds, those having rings, coils, calipers, Raschig, Intos or Pall rings, Berl or Intalox saddles, Top-Pak etc. are preferred. For example, for the extraction columns to be used according to the invention particularly suitable packages are z. B. packs of Julius Montz GmbH in D-40705 Hilden, such. For example, the pack Montz-Pak B1-350. Preferably used perforated structured packages of stainless steel sheets. Packing columns with ordered packs are known in the art and z. In Chem.-Ing.Tech. 58 (1986) No. 1, pp. 19-31 as well as in the Technical Review Sulzer 2/1979, p. 49 ff , of the Sulzer Aktiengesellschaft brothers in CH-Winterthur.

The invention further relates to a thermal separation process between at least one gas rising in a column as described above and at least one liquid descending in the column.

According to one embodiment of the method according to the invention, the liquid introduced via the return opening is introduced below the liquid level on the collecting surface.

According to one embodiment of the method according to the invention, the ascending gas and / or the descending liquid contains in particular (meth) acrylic monomers.

The thermal separation process according to the invention may e.g. a fractional condensation process for separating acrylic acid from a product gas mixture containing acrylic acid of a heterogeneously catalyzed gas phase partial oxidation of a C3 precursor compound (in particular propene and / or propane) of the acrylic acid with molecular oxygen to acrylic acid.

The separation column (condensation column) can, as in the publications DE 10243625 A1 or. WO 2008/090190 A1 be executed described, it is envisaged that at least partially the above-described circulation facilities are provided in the soils used there.

In the process according to the invention, the tendency to polymerize is particularly great due to the use of (meth) acrylic monomers. Such undesired polymerization is prevented in the process according to the invention in that the liquid collecting on the collecting surface of a mass transfer tray is pumped out through the discharge opening and is returned to the column cavity via the return opening or via the return openings.

Figur 1

zeigt schematisch einen Vertikalschnitt eines Teils einer Kolonne gemäß einem Ausführungsbeispiel der Erfindung,

Figur 2

zeigt schematisch einen Vertikalschnitt eines Teils einer Kolonne gemäß einem weiteren Ausführungsbeispiel der Erfindung,

Figur 3

veranschaulicht die vertikale Anordnung von Einrichtungen bei der Kolonne des weiteren Ausführungsbeispiels und

Figur 4

zeigt einen Querschnitt der Kolonne eines noch weiteren Ausführungsbeispiels der Erfindung.

Exemplary embodiments of the column according to the invention and exemplary embodiments of the method according to the invention are explained below with reference to the drawings.

FIG. 1

shows schematically a vertical section of a part of a column according to an embodiment of the invention,

FIG. 2

shows schematically a vertical section of a part of a column according to a further embodiment of the invention,

FIG. 3

illustrates the vertical arrangement of devices in the column of the further embodiment and

FIG. 4

shows a cross section of the column of a still further embodiment of the invention.

The embodiment described below relates to a separation column 1, as z. B. in a process of fractional condensation for the separation of acrylic acid from an acrylic acid-containing product gas mixture of a heterogeneously catalyzed gas phase partial oxidation of a C3 precursor compound (in particular propene and / or propane) of acrylic acid is used with molecular oxygen to acrylic acid.

In Fig. 1 is the known separation column 1 shown schematically. It comprises a cylindrical column body 2 whose axis is vertically aligned. The column body 2 is essentially a hollow cylinder. That is, the shell of the column body 2 forms a column cavity 3. The column body 2 is made of stainless steel. Outwardly, the separation column 1 is normally thermally isolated in a conventional manner. The height of the separation column 1 is 40 m.

In the column cavity 3 a plurality of mass transfer trays 4 are fixed, which are aligned horizontally and vertically spaced from each other. The mass transfer trays 4 serve as separating internals which improve the material separation in the separation column 1. At the in FIG. 1 shown partial view of one of the mass transfer trays 4 is shown.

The mass transfer tray 4 in this case is a chimney tray. This mass transfer tray 4 comprises a horizontally mounted in the column body 2 plate which forms the collecting surface 5 on the top. In the plate passage openings 20 are formed. In these passages 20 chimneys 6 are used. In this case, 20 fluid-tight cylindrical body 8, which are also referred to as a fireplace body, are inserted into the passage openings. Up to the upper edge 23 of the cylindrical body 8, liquid 21 can accumulate on the collecting surface 5. The opening formed within the cylindrical body 8 is covered by a cover 7, that is, the opening is shielded against dripping liquid. Such fireplace floors are known.

In the column 1 according to the invention, a circulation device 9 is now provided. This circulation device 9 comprises a drain opening 10, which is formed directly above the collecting surface 5 in the shell of the column body 2. At the drain opening 10, a circulation line 11 connects. Through the drain opening 10 liquid 21, which accumulates on the collecting surface 5, led out of the column cavity 3.

In the circulation line 11, a pump 12 is arranged, which promotes the liquid led out via the circulation line 11 to a return opening 14. The return opening 14 is arranged above the upper edge of the cylindrical body 8 of the chimneys 6. The circulation line 11 opens into this return opening 14, wherein in the return opening 14 and at the end of the circulation line 11, a nozzle 15 is arranged. Via the nozzle 15, the liquid is injected above the drain opening 10 back to the mass transfer tray 4. The circulation line 11 and the return opening 14 are arranged so that the recirculated liquid radially into the Column cavity 3 enters. The nozzle 15 is designed so that in all areas on the collecting surface 5 of the mass transfer tray 4, a liquid flow is generated, which prevents the result that long residence times of liquid volumes on the collecting surface.

According to another in FIG. 2 In the embodiment shown, the return opening 14 is arranged at the same height as the discharge opening 10 or at least below the upper edge 23 of the cylindrical body 8 of the chimneys 6. The return opening 14 is arranged in this case, optionally below the liquid level 22 on the collecting surface 5. In this case, a so-called propulsion jet nozzle 15 is arranged in the return opening 14, through which the liquid is injected into the standing liquid 21, whereby a liquid flow is generated on the collecting surface 5.

The other facilities of the circulation device 9 are in FIG. 2 not shown for reasons of clarity. They are the same as they are already related to FIG. 1 have been described.

Based on FIG. 3 For example, possible vertical arrangements of the collecting surface 5, the discharge opening 10, the return opening 14, the liquid level 22, the upper edges 23 of the cylindrical body 8 and the bottom 26 of the immediately above the mass transfer tray 4 are illustrated. The collecting surface 5 is at the height L1, the lower edge 24 of the drain opening 10 is at the height L2 and the upper edge 25 of the rear opening 14 is arranged at the height L3. The liquid level 22 is arranged at the height L4. The cylindrical body 8 of the chimneys 6 form at their upper edges 23 overflow edges. The lowest overflow edge of the cylindrical body 8 is arranged at the height L5. The underside 26 of the immediately above the collecting surface 5 arranged mass transfer tray 4 is arranged at the height L6.

In the embodiment of the FIG. 3 the return opening 14 and the drain opening 10 are arranged between the two adjacent mass transfer trays 4 and below the liquid level 22. Further, the ratio of the vertical distance of the collecting surface 5 of the mass transfer tray 4 from the lower edge 24 of the discharge port 10 to the vertical distance of the collecting surface 5 of the mass transfer tray 4 from the height L5 of the lowermost overflow edge of the cylindrical body 8 in a range of 0 to 0 , 1, ie: $$0\le \frac{\mathit{Section}\left(L1-\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">L</figure-callout>}2\right)}{\mathit{Section}\left(L1-\mathrm{<figure-callout\; id="5"\; label="L"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">L</figure-callout>}5\right)}\le 0.1$$

Further, the ratio of the vertical distance of the collecting surface 5 of the mass transfer tray 4 from the upper edge 25 of the return opening 14 to the vertical distance of the collecting surface 5 of the mass transfer tray 4 from the height L5 of the lowest overflow edge of the cylindrical body 8 is in a range from 0 to 0, 9, ie: $$0\le \frac{\mathit{Section}\left(L1-\mathrm{<figure-callout\; id="3"\; label="L"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">L</figure-callout>}3\right)}{\mathit{Section}\left(L1-\mathrm{<figure-callout\; id="5"\; label="L"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">L</figure-callout>}5\right)}\le 0.9$$

If the collecting tray 4 is not a chimney tray but a differently shaped collecting tray 4, which has no cylindrical body 8, the ratio of the vertical distance of the collecting surface 5 of the mass transfer tray 4 from the lower edge 24 of the discharge opening 10 to the vertical distance of the collecting surface 5 of the mass transfer tray 4 from the bottom 26 of the immediately above arranged mass transfer tray 4 in a range of 0 to 0.3, that is it applies: $$0\le \frac{\mathit{Section}\left(L1-\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">L</figure-callout>}2\right)}{\mathit{Section}\left(L1-\mathrm{<figure-callout\; id="5"\; label="L"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">L</figure-callout>}5\right)}\le 0.3$$

Further, the ratio of the vertical distance of the collecting surface 5 of the mass transfer tray 4 from the upper edge 25 of the return port 14 to the vertical distance of the collecting surface 5 of the mass transfer tray 4 from the bottom 26 of the immediately above the mass transfer tray 4 in a range of 0 to 0.3 ie: $$0\le \frac{\mathit{Section}\left(L1-\mathrm{<figure-callout\; id="3"\; label="L"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">L</figure-callout>}3\right)}{\mathit{Section}\left(L1-\mathrm{<figure-callout\; id="5"\; label="L"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">L</figure-callout>}5\right)}\le 0.3$$

According to further embodiments, other configurations of the collecting surface of the mass transfer tray 4 relative to the drain opening 10 can be selected. For example, a channel formed in the mass transfer tray 4 can open into the discharge opening 10. Furthermore, the circulation line 11 can open into a plurality of return openings 14.

The circulation line 11 further includes a junction 13. At this junction 13 opens a supply line 16 for a further liquid in the circulation line 11 on. The supply line 16 has a valve 17, via which the liquid supply can be controlled or regulated in the circulation line 11.

In FIG. 4 is a cross section at the height of the return opening 14 of the column 1 according to the invention shown. It shows FIG. 4 a still further embodiment in which not only a return opening 14 is formed in the column body 2, but a plurality of return openings 14-1, 14-2 and 14-3. These return openings 14-1 to 14-3 are connected via a ring line 18 to the circulation line 11. The return openings 14-1 to 14-3 are arranged in this case relative to the chimneys 6 so that a meandering liquid flow 19 results on the collecting surface 5 of the mass transfer tray 4. The return openings 14-1, 14-2 and 14-3 and the drain opening 10 can be as above with reference to FIG. 3 explained to be arranged in a vertical sense.

It should be noted that in all embodiments, other of the initially mentioned mass transfer trays can be used.

In the following, an embodiment of the method according to the invention will be described, which is carried out with the above-described separation column 1 of one of the embodiments.

The process is a thermal separation process between at least one gas rising in the separation column 1 and at least one liquid descending in the separation column 1. In particular, the ascending gas and / or the descending liquid contains (meth) acrylic monomers.

In the separation process, a fractional condensation is carried out to separate acrylic acid from a product gas mixture containing acrylic acid of a heterogeneously catalyzed gas phase partial oxidation of a C3 precursor compound (in particular propene and / or propane) of the acrylic acid with molecular oxygen to acrylic acid in a separating column 1 containing separating internals. The separation column 1 contains from bottom to top several mass transfer trays 4. For example, initially dual-flow trays and then cross-flow hood floors or chimney trays are arranged, in which at least in part a respective circulation device 9 is formed, as described above. Otherwise the procedure is carried out as described in the scriptures DE 19924532 A1 . DE 10243625 A1 and WO 2008/090190 A1 is described. However, liquid is continuously pumped from the collecting surfaces 5 of the mass transfer trays 4 by means of the circulation means 9 and the collecting surfaces 5 at the respective mass transfer tray 4 fed back via the return opening 14 or the return openings 14-1 to 14-3.

The term "C3 precursor" of acrylic acid is taken to mean those chemical compounds which are obtainable formally by reduction of acrylic acid. Known C3 precursors of acrylic acid are e.g. Propane, propene and acrolein. But also compounds such as glycerol, propionaldehyde, propionic acid or 3-hydroxypropionic acid are among these C3 precursors count. From them, the heterogeneously catalyzed gas phase partial oxidation with molecular oxygen is at least partially an oxidative dehydrogenation. In the relevant heterogeneously catalyzed gas phase partial oxidations, said C3 precursors of acrylic acid, typically with inert gases such as e.g. diluted molecular nitrogen, CO, CO2, inert hydrocarbons and / or steam, passed in admixture with molecular oxygen at elevated temperatures and optionally elevated pressure over transition metal mixed oxide catalysts and oxidatively converted into an acrylic acid-containing product gas mixture.

Typically, the acrylic acid-containing product gas mixture of a heterogeneously catalyzed gas phase partial oxidation of C3 precursors (eg propene) of acrylic acid with molecular oxygen to solid state catalysts, based on the total amount of (indicated in) specified constituents, the following contents : 1 to 30% by weight Acrylic acid, 0.05 to 10% by weight molecular oxygen, 1 to 30% by weight Water, 0 to 5% by weight Acetic acid, 0 to 3% by weight propionic acid, 0 to 1% by weight Maleic acid and / or maleic anhydride, 0 to 2% by weight acrolein, 0 to 1% by weight Formaldehyde, 0 to 1% by weight furfural, 0 to 0.5% by weight benzaldehyde, 0 to 1% by weight Propen, and as residual amount of inert gases such as nitrogen, carbon monoxide, carbon dioxide, methane and / or propane.

The partial gas phase oxidation itself can be carried out as described in the prior art. Starting from propene, the partial gas phase oxidation for example, be carried out in two successive oxidation stages, as for example in the EP 700 714 A1 and in the EP 700 893 A1 are described. Of course, but also in the DE 19740253 A1 as well as in the DE 19740252 A1 cited gas phase partial oxidations are used.

In general, the temperature of the product gas mixture leaving the partial gas phase oxidation is 150 to 350 ° C., frequently 200 to 300 ° C.

By direct and / or indirect cooling, the hot product gas mixture is expediently first cooled to a temperature of 100 to 180 ° C, before it is conducted for the purpose of fractional condensation in the region C (the bottom) of the separation column 1. The pressure prevailing in the separation column 1 operating pressure is usually 0.5 to 5 bar, often 0.5 to 3 bar and often 1 to 2 bar.

LIST OF REFERENCE NUMBERS

1

Column, separation column

2

column body

3

column cavity

4

Mass transfer tray

5

collecting area

6

fireplace

7

cover

8th

cylindrical body; fireplace body

9

circulation means

10

drain hole

11

circulation line

12

pump

13

junction

14

Return port;

14-1 to 14-3

Return opening

15

Jet; propulsion

16

feed

17

Valve

18

loop

19

liquid flow

20

Through openings

21

liquid

22

liquid level

23

upper edge of the cylindrical body

24

lower edge of the drain hole

25

upper edge of the return opening

26

Bottom of the above arranged mass transfer tray

Claims (15)

1. A column (1) for thermal treatment of a fluid, having a cylindrical, vertical column body (2) which forms a column cavity (3), and a mass transfer tray (4) which is disposed in the column cavity (3) and forms a collecting area (5), and
   a circulation device (9) having at least one drain orifice (10) formed in the column body (2) above the collecting area (5), a circulation line (11) in fluid connection with the drain orifice (10) and at least one recycling orifice (14; 14-1 to 14-3) which is in fluid connection with the circulation line (11) and is formed in the column body (2) above the collecting area (5), wherein
   the mass transfer tray (4) has passage orifices (20) for gas ascending from the bottom, and cylindrical bodies (8) extend upward in the passage orifices (20), where
   the upper edges (23) of the cylindrical body (8) form overflow edges and the ratio of the vertical distance of the lowest region (L1) of the collecting area (5) of the mass transfer tray (4) from the upper edge (25) of the recycling orifice (14; 14-1 to 14-3) to the vertical distance of the lowest region (L1) of the collecting area (5) of the mass transfer tray (4) from the height (L5) of the lowermost overflow edge of the cylindrical bodies (8) is within a range from 0 to 0.9, especially within a range from 0 to 0.3.
2. The column (1) according to claim 1,
   wherein
   the lower edge (24) of the drain orifice (10) is disposed immediately above the lowermost region of the collecting area (5) of the mass transfer tray (4).
3. The column (1) according to claim 1 or 2,
   wherein several vertically spaced-apart mass transfer trays (4) are disposed in the column cavity (3) and the drain orifice (10) and the recycling orifice (14; 14-1 to 14-3) are arranged vertically between two adjacent vertically spaced-apart mass transfer trays (4).
4. The column (1) according to claim 3,
   wherein
   the ratio of the vertical distance of the lowest region (L1) of the collecting area (5) of the mass transfer tray (4) from the lower edge (24) of the drain orifice (10) to the vertical distance of the lowest region (L1) of the collecting area (5) of the mass transfer tray (4) from the underside (26) of the mass transfer tray (4) disposed immediately above it is within a range from 0 to 0.3, especially within a range from 0 to 0.1.
5. The column (1) according to any of the preceding claims,
   wherein
   the recycling orifice (14; 14-1 to 14-3) opens into the column cavity (3) above the drain orifice (10).
6. The column (1) according to any of claims 1 to 4, wherein
   the recycling orifice (14; 14-1 to 14-3) opens into the column cavity (3) at the same height as the drain orifice (10).
7. The column (1) according to either of claims 3 and 6,
   wherein
   the ratio of the vertical distance of the lowest region (L1) of the collecting area (5) of the mass transfer tray (4) from the upper edge (25) of the recycling orifice (14; 14-1 to 14-3) to the vertical distance of the lowest region (L1) of the collecting area (5) of the mass transfer tray (4) from the underside (26) of the mass transfer tray (4) disposed immediately above it is within a range from 0 to 0.3, especially within a range from 0 to 0.2.
8. The column (1) according to any of the preceding claims,
   wherein
   the circulation line (11) and the recycling orifice (14; 14-1 to 14-3) are arranged such that the liquid recycled enters the column cavity (3) radially.
9. The column (1) according to any of the preceding claims,
   wherein
   a plurality of spaced-apart recycling orifices (14-1, 14-2, 14-3) are formed in the column body (2), each of which is in fluid connection with the circulation line (11) this.
10. The column (1) according to any of the preceding claims,
    wherein
    the upper edges (23) of the cylindrical body (8) form overflow edges and the ratio of the vertical distance of the lowest region (L1) of the collecting area (5) of the mass transfer tray (4) from the lower edge (24) of the drain orifice (10) to the vertical distance of the lowest region (L1) of the collecting area (5) of the mass transfer tray (4) from the height (L5) of the lowermost overflow edge of the cylindrical bodies (8) is within a range from 0 to 0.1, especially within a range from 0 to 0.05.
11. The column (1) according to any of the preceding claims,
    wherein
    the recycling orifices (14-1, 14-2, 14-3) are arranged relative to the cylindrical bodies (8) so as to result in a meandering liquid flow (19) on the collecting area (5) of the mass transfer tray (4).
12. The column (1) according to any of the preceding claims,
    wherein
    the mass transfer tray (4) is a chimney tray and the cylindrical body (8) is a chimney body.
13. A thermal separation process between at least one gas ascending within a column (1) according to any of claims 1 to 12 and at least one liquid descending within the column (1).
14. The process according to claim 13,
    wherein
    liquid is introduced via the recycling orifice (14; 14-1 to 14-3) below the liquid level (22) on the collecting surface (5).
15. The process according to claim 13 or 14,
    wherein
    the ascending gas and/or the descending liquid comprises (meth)acrylic monomers.

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